1. Focus-Point studies at LHC
U. De Sanctis, T. Lari, C. Troncon
University of Milan and INFN
ATLAS Collaboration
Focus-Point studies at LHC
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point

2. SUSY and Dark Matter DM  SUSY
Non-baryonic matter density, computed from WMAP measurements:
0.094 < WDM h2 < (2s confidence interval)
For any specific set of parameters of a SUSY R-parity conserving model, it is
possible to compute the LSP relic density from the mass spectrum and the Big-Bang
cosmology.
The relic density can be less than WDM (if other contributions to the DM).
The WMAP upper limit is a constrain that defines cosmologically interesting
regions of the SUSY parameter hyperspace.
I will limit myself to mSUGRA here.
SUSY  DM
Once (if) we will have a measurement of SUSY mass spectrum mixing angle etc.,
one can compute the relic density it corresponds to.
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

3. mSUGRA and DM SUSY spectrum computed with ISAJET 7.69
In most of mSUGRA
parameter space the
predicted relic density
is too large.
In the Focus-Point region
(large m0) the lightest
neutralino has a significant
Higgsino component, and
the relic density is reduced
by s-channel annihilation
in the early universe.
SUSY spectrum computed with ISAJET 7.69
Relic density computed with Micromegas 1.3.0
Focus Point
Coannihilation
(very narrow)
Selected for a detailed study with ATLAS simulation.
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

4. Comparison of RGE codes
m0 scan
m1/2 = 300 GeV tanb = 10 A0=0 m >0 mt=175 GeV
Large differences in the predicted
relic density using different codes
to compute SUSY mass spectrum
at the Electro-Weak scale.
The study presented here was
made using ISAJET 7.69.
Wh2
3000
4000
m0 (GeV)
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

5. SUSY mass spectrum Mass spectrum at the selected point Masses (GeV) ~
M0=3400 GeV m1/2 = 300 GeV tanb = 10 A0=0 m >0 mt=175 GeV
Masses (GeV) ~
c01
102.6
c02
157.4
c03
172.3
c04
290.5
c1
145.4
c2
282.7 g
854 qL
3416 t1
2041 h
118. 8 ~ ~ ~ ~ ~ ~ ~ ~
Squarks at the limit of LHC reach. Other sleptons and heavy Higgs too heavy for LHC.
Gluino decays into neutralinos and charginos.
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

6. Production xSection Sum of jet and missing transverse energy.
using ATLAS fast simulation
Production xSections ~ ~ cc
4.6 pb gg
0.58 pb qg
3.7 fb ~ ~ ~ ~
10 fb-1 (1st LHC year?)
Susy/√SM = 16
cc production most abundant,
but little jet and missing energy:
difficult to separate from SM. We are
investigating the possibility to use
c±1c02 → c01 l± c01 l+ l-
searching for 3 leptons+missing
energy+no jet events.
gluino pair production dominant
after standard SUSY cuts.
squarks visible with high luminosity
Standard cuts (not optimized for this point)
on jet and missing energy and lepton veto.
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

7. Gluino decays Gluino decays: g → c0 qq 7.2 % g → c0 bb 3.7 %
g → c0 tt %
g → c0 g %
g → c qq %
g → c tb %
Golden channel is the neutralino dilepton decay
(gives neutralino mass difference).
In principle, the leptons from neutralino decays can be combined with jets to get further mass relations.
However, large number of jets from gluino decay (heavy combinatory background) and poor lepton statistics to start with.
We have concentrated on reconstruction of the two
main gluino decays using tt and tb invariant mass
distributions (gives difference between gluino and
gaugino mass scales)
Neutralino dilepton decays:
c03 → c01 l l
c02 → c01 l l
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

8. Dilepton mass distributions
The c02 edge can be measured (constrain
on neutralino mixing matrix from the shape?)
The c03 edge hardly visible even after three
years at design luminosity.
At generator level
ATLAS ~ ~
c02 → c01 l+l-
Experimental, flavour subtracted ~ ~ ~ ~
c03 → c01 l+l-
ATLAS ~ 20 40 60
Mll (GeV)
300 fb-1
No SM background
Cuts: Meff > 750 GeV, ETmiss > 100 GeV,
1 jet with pT > 100 GeV
Leptons with pT > 10 GeV 20 40 60 80
Mll (GeV)
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

9. Gluino decays to chargino
Top quark decay into udb or csb fully reconstructed.
tb invariant masses reconstructed.
30 fb-1
No SM background
ATLAS
M(g)-M(c1)
33 fb-1
no SM backg.
M(g)-M(c2)
200
400
600
Mtb (GeV)
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

10. Gluino to neutralino g → c04 tt g → c03 tt g → c02 tt g → c01 tt
Invariant mass of two fully reconstructed tops.
Analysis cuts similar to the gluino to chargino analysis.
With high luminosity an endpoint can be extracted.
At generator level
Experimental, flavour subtracted
ATLAS
ATLAS ~ ~
g → c04 tt
300 fb-1
No SM background ~ ~
g → c03 tt ~ ~
g → c02 tt ~ ~
g → c01 tt
400
600
800
400
600
800
Mtt (GeV)
Mtt (GeV)
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

11. Scan of parameter space
As one moves up the FP strip the SUSY masses
increase and the production cross sections decrease.
FP2
FP3
FP4
FP5 M0
3400
4200
5720
6000
M1/2
300
500
1000
Wh2
.059
.026
.078
.012
M(g)
854
1334
2453
2468
M(c01)
103
176
401
241
s(gg)
580
21.3
0.05
s(cc)
4600
1074 57
480
s(gq)
3.7
0.2
M0-m1/2 scan for mt=175 GeV,A0=0,tanb=10,m>0
FP5
FP4
Gluino mass
FP3
FP2
Cross sections in fb, masses in GeV
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

12. Neutralino mass differences
The c02 is close in mass to c01 on the right of the band (where W << WWMAP) while
it is close to the c03 on the left of the band (where W ~ WWMAP).
Almost always m(c02)-m(c01) is below the threshold for c02 → c01 Z0
The dilepton edge would provide a good constrain on W.
M(c02)-M(c01)
M(c03)-M(c02)
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

13. Effect of top mass M1/2 (GeV) M1/2 (GeV) Mt = 175 GeV 500 500
100
100
2000
5000
2000
4000
M0 (GeV)
As the top mass is increased the FP
region moves to larger values of m0.
For the same m1/2 the gluino/gaugino
masses and decays depend very little
on the top mass.
Sfermions are within LHC reach only
for a light top.
Mt = 178 GeV
500
100
2000
5000
M0 (GeV)
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

14. Effect of top mass At fixed m1/2 = 300 GeV, relation between
mtop and m0 for the FP region.
tanb=10,A0=0,m>0
FP6
FP2
FP7
FP8
mtop
172
175
178
183 M0
1900
3400
7130
30850
M1/2
300
Wh2
.066
.059
.077
.0827
M(g)
814
854
904
1011
M(c01)
102
103
108
106
s(gg)
703
580
412
202
s(cc)
4610
4600
3650
4130
s(gq)
110
3.7
FP8
FP7
FP2
FP6
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

15. Effect of tanb tanb=10 tanb=54 FP2 FP10 FP11 tanb=30
A larger value of tanb pushes the FP band
to lower values of m0
At FP11 abundant squark production!
FP9
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

16. Conclusions
Part of the Focus-Point region is accessible by the LHC experiments. A test
point was studied with the ATLAS detector fast simulation. A number of mass
constrains can be measured: m(c02)-m(c01), m(g)-m(c±) and m(g)-m(c0).
A scan of mSUGRA focuspoint space has been performed with ISAJET to study how the SUSY mass spectrum varies and select points for more detailed studies.
The gluino gets heavier as one moves along the band in the m0-m1/2 plane. The LHC reach to observe gluino pair production should be about m1/2 ~ 900 GeV. Gaugino production may be used to extend this reach, assuming it can be isolated from the SM background.
The neutralino spectrum is sensitive to position both along and trasversal to the band.
The squarks are accessible for low top masses and/or high tanb - this would allow to get m0 (and confirm that sfermions are there…)
The Focus-Point is under active study by the ATLAS collaboration. All results are preliminary and more are coming.
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

17. Horizontal line scan (III)
Not really any good solution with SOFTSUSY
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

18. Comparison of RGE codes (2)
Comparison for point
M0=3400 GeV m1/2 = 300 GeV tanb = 10 A0=0 m >0 mt=175 GeV
ISAJET 7.69
SOFTSUSY 1.86
SPheno 2.22
Suspect 2.3
M(c01)
102.6
126.9
127.0
M(c02)
157.4
247.7
248.6
247.4
M(c03)
172.3
596.4
665.4
580.8
M(g)
853.7
858.1
807.7
869.0
M(uL)
3419
3481
3431
All masses in GeV
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies

19. One more table Little effect from changing the sign of m
FP12
FP2
FP9
FP10
FP11
mtop 10 30 54 M0
3400
2400
2300
1400
M1/2
300
180 m - + W
.061
.059
.091
.052
.114
M(g)
854
829
825
517
M(uL)
3416
2449
2356
1435
M(t1)
2041
1479
1427
860
M(c01)
111
103
107 68
s(gg+gq)
580
700
1314
16670
s(cc)
4550
4610
4600
3650
4130
Little effect from changing the sign of m
mh = GeV
EuroGDR
Frascati 25/11/2004
T. Lari
Focus Point studies